Structural Question HVAC openings 1

[UtahAggiePE]

Forgive my ignorance. I do structural engineering and have very little knowledge about HVAC. I often work on commercial buildings that may have large HVAC units on the roof or beside the building. When designing components and cladding the internal/external pressures of the building determine the forces on the cladding (like windows). The code requires us to consider openings into buildings that would allow air to enter or escape in high winds.

Am I correct in my assumption that the HVAC equipment is designed to prevent high winds from pressurizing or depressurizing a building through air intakes/vents etc?

 

[EnergyProfessional]

Most HVAC openings typically have a louver, fan, dampers and other devices that create pressure drop. So it would be much less than just a plain opening. Many are also controlled to modulate the damper to maintain a specific air flow.

Note that the building enclosure itself is not air-tight and you have added building pressure due to wind forces, and stack effect. But I doubt they are large enough to be significant for structural integrity.

 

[UtahAggiePE]

I wonder about stack effect, it must be small since the building code doesn't mention it at all, or it is baked-in since taller buildings have higher net pressures to consider. I'm sure it is a combination of higher winds at higher elevations as well as internal pressures due to a variety of factors.

It is a challenge on where to draw the line with louvers etc since an opening on one side of the building can act like the opening for a balloon to radically change the internal pressures (despite the permeability of the building envelope.) It isn't an exact science the way us civil engineers analyze it and the penalty for openings can be extreme.

 

[EnergyProfessional]

Infiltration is measured at 75 Pa, which is artificially high to get better test results. Real world pressurization will be below that. I hope the buildings you design can withstand 75 Pa

 

[UtahAggiePE]

Haha, I think we can manage that.

 

[AdrienneGC]

Some manufacturers rate their louvers for HVHZ or other high-velocity designation.

Adrienne Gould-Choquette, P.E.

http://www.adicot.com